U.S. Pat. No. 5,086,084, issued to Michaelson, teaches a foamed polymeric material suitable as a wood substitute, made of a continuous phase of polyurethane having solid polyvinyl chloride particles dispersed therein. The wood-like material of Michaelson is said to contain about 100 parts of a foamable urethane, and 10 to 50 parts polyvinyl chloride (PVC) particles having a particle size below 200 μm. This material has a microcellular structure with cells on the order of 0.1 mm in average diameter or less. The walls are said to be made of a matrix of polyurethane reinforced with PVC particles. Michaelson, however, makes no mention of the heat performance properties of his wood substitute.
Mushovic, in U.S. Pat. Nos. 5,302,634, 5,369,147, 5,508,315 and 5,604,266, teaches rigid, lightweight filled resin foams having voids dispersed in a continuous phase which is formed from a polyester polyol-polyurethane hybrid resin having reinforcing particles dispersed therein. The hybrid resin of Mushovic is said to form an interpenetrating polymer network with a polyurethane and/or a modified hybrid polyurethane resin. The foams of Mushovic are said to be useful in building materials requiring high tensile and compressive strengths and corrosion and thermal resistance.
U.S. Pat. No. 6,211,259, issued to Borden et al., teaches compositions for making polyurethane and polyurethane foam compositions. These compositions are the reaction product of an isocyanate and a B-Side made of: (i) a polyol having a molecular weight of about 1,000 g/mol or more, and having an average functionality of 2.0 or greater; (ii) a polyol having a Tg of about −80° C. or less, and having a molecular weight of about 1,000 g/mol or more, and having an average functionality of 2.0 or greater; and (iii) a polyhydric alcohol having a molecular weight of about 90 g/mol or more, and having an average functionality of 3.0 or more.
U.S. Pat. No. 6,265,457, issued to Dolgopolsky et al., teaches an isocyanate-based polymer foam made from an isocyanate-based polymer foam matrix having disposed therein a particulate material (such as polyethylene) having an enthalpy of endothermic phase transition of at least about 50 J/g. During the process of Dolgopolsky et al., the particulate material is said to act as a heat sink and undergo an endothermic phase change by absorbing a significant portion of the heat of reaction liberated during the process. Dolgopolsky et al. teach that the heat absorption improves the safety of the process by lowering the maximum exotherm experienced by the foam and/or improves product properties.
Lundgard et al., in U.S. Pat. No. 6,613,827, teach a process for preparing a stable dispersion of a preformed polymer in a polyol in a single mixer. A preformed polymer is mixed under sufficient heat and shear to reduce its particle size to a desired size in the presence of a polyol. The invention of Lundgard et al., also provides stable dispersions of polymers in polyols and polyurethane formulations containing stable dispersions made by their process.
A need continues to exist in the art for improved rigid polyurethane foams, such as those having increased heat performance (i.e., decreased heat sag), which also maintain other desired physical properties.